US3921577A

US3921577A - Magnetic development units

Info

Publication number: US3921577A
Application number: US473651A
Authority: US
Inventors: Willard L Howard; Thomas A Tietjen
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1974-05-28
Filing date: 1974-05-28
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25
Also published as: NL7505331A

Abstract

To improve magnetic brush and magnetic transport cascade-type development units for electrostatic copiers and the like, there is a resilient baffle for suppressing uncontrolled emissions of toner while leveling the profile of the magnetically entrained developer material.

Description

United States Patent 1191 Howard et al.

MAGNETIC DEVELOPMENT UNITS inventors: Willard L. Howard, Marion;

Thomas A. Tietjen, Rochester, both of NY.

Xerox Corporation, Stamford. Conn.

Filcd: May 28, 1974 Appl. No.: 473,651

Assignee:

US. Cl. 118/637 Int. Cl. G03G 15/08 Field of Search 118/637, il7/l7.5

Relerences Cited UNiTED STATES PATENTS 3/l960 Oldenboom 8/637 1 Nov. 25, 1975 3,428,025 2/l969 Sullivan, Jr. ll7/i7.5 3,572,289 3/1971 3,64l,980 2/1972 3,649,262 3/l972 3,724,422 4/1973 Latone et al 1 18/637 Primary Examiner-W. C. Reynolds Assistant Examiner-Douglas Salser [57] ABSTRACT To improve magnetic brush and magnetic transport cascade-type development units for electrostatic copiers and the like. there is a resilient baffle for suppressing uncontrolled emissions of toner while leveling the profile of the magnetically entrained developer material.

7 Claims, 4 Drawing Figures Sheet 1 of 2 US. Patent Nov. 25, 1975 U.S. Patent Nov. 25, 1975 Sheet 2 of FIG. 3b

MAGNETIC DEVELOPMENT UNITS BACKGROUND OF THE INVENTION This invention relates to development units forielec-j trostatic copiers and duplicators (hereinafter collectively referred to as copiers") and. more particularly.

" substantially full width. flexible baffles are included in to means for suppressing uncontrolled'emissions off toner from development units for continuous copiers.

In a conventional electrostatic copying process of the type disclosed in Carlson U.S. Pat. No. 2.297.691 on Electrophotography." a uniformly charged photoreceptor is selectively discharged in an imagewise configuration to provide a latent electrostatic image which is subsequently developed by means of a finely divided, lightweight. electroscopic marking material, called "toner." This process has enjoyed outstanding commercial success. especially in continuous copiers. Nevertheless. substantial effort and expense are still being devoted to the perfection of development units for applying the toner on the fly as the photoconductor moves through a development zone.

Magnetic brush and magnetic transport cascadetype development units have both shown substantial promise for use in continuous copiers. They employ a developer material which normally includes triboelectricaily charged toner in combination with a relatively coars. granular magnetic material. such as ferrite beads. In operation; the magnetic component carries the toner from a sump to the development zone where toner is electrostatically stripped from the. magnetic carrier to develop the latent image. Thereafter the partially denuded carrier is returned to the sump for recirculation.

Continuity is achieved by adding new toner to the sump from time-to-time to replace the toner consumed in the development process. Preferably. the additional toner is added automatically while the copier is in operation. However. it has been found that there sometimes are uncontrolled. powder cloud-like emissions of toner from the toner addition regions of magnetic brush and magnetic transport cascade-type development units due to the air currents generated by the motion of the photoconductor. developer. and developer transport system. Unfortunately. those emissions have the undesired effect of increasing the background development levels of the ultimate copies.

SUMMARY OF THE INVENTION Accordingly. an object of this invention. is to provide means for suppressing uncontrolled emissions of toner from development units for electrostatic copiers. More particularly. an object is to provide means for containing airborne particles of toner within such a development unit.

Even more specifically, an object of the presentinvention is to provide a self-sealing baffle for suppressing uncontrolled emissions of toner from magnetic brush and magnetic transport cascade-type development units for continuous copiers. A more detailed object is to provide a b'affle which not only accomplishes that function. but which also improves the uniformity of the development process by aiding in leveling the profile of the magnetically entrained developer mate'- rial.

Another object of this invention is to provide a reliable and relatively inexpensive self-sealing baffle for carrying out the above-mentioned functions in new and the' .ill ustrated magnetic brush and magnetic transport cascade-type developme'nPunits. Each of the baffles "II88 on'e'side anchored tq the housing for the developer unit and its'opposite. free side biased into engagement with the magnetically entrained developer material. Preferably. the free sides of the baffles are arcuate so that each of them presents a continuous. edge free. contact surface for leveling the profile of and seating against the development material without any appreciable scraping action.

BRIEF DESCRIPTION OF THE DRAWINGS Still further objects and advantages of the present invention will become apparent when the following detailed description is read in conjunction with the attached drawings, in which:

FIG. 1 is a fragmentary. sectional view of a continuous electrostatic copier including a magnetic brush development unit embodying the present invention;

FIG. 2 is another fragmentary, sectional view of a continuous electrostatic copier including a magnetic transport cascade-type development unit embodying the present invention;

FIGS. 3A and 3B are schematic views illustrating the profile of the magnetically entrained developer on the upstream side and the downstream side. respectively. of the baffle in the development unit shown in FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS While the invention is described in some detail hereinafter with specific reference to certain embodiments. it is to be understood that the intent is not to limit it to those embodiments. On the contrary, the intent is to cover all modifications. aitematives and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Turning now to the drawings, and at this point especially to FIG. I, it will be seen that there is a magnetic brush development unit II for applying toner l2 to a photoconductor 13 on the fly so that any latent electrostatic images on the photoconductor 13 are developed as it moves through a development zone 14. In this instance. the photoconductor i3 is coated on a flexible belt 15, but it will be apparent that the principles of this invention are equally applicable to development units for drum-type machines. Regardless of the machine configuration, the toner 12 is typically delivered to the development zone I4 as one component of a developer material 16 which conventionally comprises triboelectrically charged toner particles bonded to relatively coarse. gran'ular particles of magnetic material. such as ferrite beads.

. In accordance with the present invention. the development unit ll includes a flexible baffle 17 for suppressing uncontrolled emlsslons of toner 12 while levcling the profile of the developer l6 delivered to the development zone 1. Otherwise. however. it is essentially the same as the unit described and claimed in a co-pending and commonly assigned United States Patent application filed Jan. l7. 1973. by F.W. Hudson under Ser. No. 324,467 on a Toner Preloaded Magnetic Brush Development System."

More particularly, as illustrated, the development unit 11 comprises a housing 21 which opensoutwardly toward the photoconductively coated side of the belt 16 to define the development zone 14. inside the housing 21, there-are a plurality-of elongated, permanent magnets 22-26, which are supported-"within separate non-magnetic, tubular rolls 27-31, respectively, adja-- cent the development zone 14 and in spaced-apart rela'-" tionship along the path of travel of the photoconductor 13 therethrough. Each of the magnets 22-26 extends across substantially the full width of the development zone 14 and is held in a fixed position. Each of the rolls 27-31 also extends across substantially the full width of the development 'zone 14, but means (not shown) are provided for rotating adjacent ones of them in opposite directions.

in operation. the magnetic field created by the magnets 22-26 entrains a portion of the development material 16 which is nominally stored in a sump 32 at the bottom of the housing 21 adjacent the lowermost roll 27. The rotation of the rolls 27-31 causes the magnetically entrained developer material 16 to snake upwardly through the development unit 11 so that it is brought into brushing engagement with the photoconductor 13 by the

rolls

27, 29 and 31. After the developer material 16 passes between the photoconductor 13 and the uppermost roll 31, it is released from the magnetic field so that it drops onto an inclined guide plate 33 which returns it to the sump 32 for recirculation. A

To maintain the toner concentration at a suitably high level, there is a generally conventional toner dispenser 34 mounted on top of the housing 21 for adding toner 12 to the partially denuded developer 16 flowing along the guide plate 33. Most of the additional toner 12 ultimately becomes a part of the developer material 16, but some of it tends to remain airborne or to otherwise collect in the toner addition region 35 of the housing 21. This collection of free toner 12 is a potential source of uncontrolled, powder cloud-like emissions of toner in view of the air currents generated by the mpvement of the photoconductively coated belt 15, rolls 22-26, and developer 16.

To suppress uncontrolled emissions of free toner, one side of the baffle 17 is secured to the interior of the housing 21 slightly forward of the sump 32 and its opposite, free side is biased into engagement with the developer material 16 magnetically entrained on the lowermost roll 27. The baffle 17 extends across substantially the full width of the developer unit 11 to effectively seal the gap between the housing 21 and the roll 27. if need be, similar baffles may be used to seal other gaps, but this one amply illustrates the invention.

in keeping with one of the more detailed features of this invention, the free side of the baffle 17 is arcuate so that it presents a continuous, edge free, contact surface for engaging the magnetically entrained developer material 16. Preferably, the baffle 17 is formed from a non-magnetic, resilient material, such as one mil thick brass shim stock, so that it is self-biasing and does not upset the pattern of the magnetic field created by the magnets 22-26. in this instance, the bsflle 17 extends over and outwardly from a metering bar 40 to aid in leveling the profile of the magnetically entrained developer material 16, without any significant scraping action. Hence, the baffle 17 seals against the developer material 16 without flicking any significant amounts of the developer out of the development unit 11.

Referring to FIG. 2, it will be apparent that the present invention may also be used to advantage in magnetic transport cascade-type development units. The particular development unit 41 selected to illustrate that includes a pair of

baffles

42 and 43 in accordance with this invention, but is otherwise the same as the unit that is described and claimed in a commonly assigned U.S. Pat. No. 3,641,980 of J. T. Bickmore, which issuedFeb. 1S, 1972.

More specifically, the development unit 41 comprises a housing 44 which opens outwardly toward a photoconductively coated drum 45 to define a development zone 46. inside the housing 44, there are two assemblies of

permanent magnets

47 and 48, which are mounted within separate non-magnetic, tubular rolls 49 and 50, respectively. For illustrative purposes, a heavy line has been used to denote the north poles of the individual magnets of the two

assemblies

47 and 48.

The

magnetic assemblies

47, 48 and the rolls 49, extend across substantially the full width of the development zone 46. in operation, the

magnetic assemblies

47 and 48 are held in fixed positions, but the rolls 49 and 50 are driven (by means not shown) in opposite disections so that developer material 51 is magnetically transported from a sump 52 in the lower reaches of the housing 44 to a position above a development electrode 53. At that point, the developer 51 is released from the magnetic field and then directed by a guide .plate 54 so that it flows between the photoconductively coated drum 45 and the development electrode 53. Toner is, of course, stripped from the developer material 51 as it cascades across the drum 45 to develop any latent electrostatic image on the photoconductive coating 55. Again, therefore, provision is made for adding additional toner to the developer material 51 from time-to-time. To accomplish that, in this embodiment, there are a series of

chutes

55 and 56 for guiding the additional toner from a toner dispenser (not shown) into the sump 52.

In keeping with this invention, the

baffies

42 and 43 suppress uncontrolled emissions of toner and level the profile of the developer material 51 delivered to the development zone 46. To that end, the baffle 42 has one side secured to the housing 44 just in front of the sump 52 and its opposite, free side biased into engagement with the magnetically entrained developer material 51 on the lower roll 49. The baffie 43, on the other hand, has one side secured to the housing 44 in the area above the roll 50 and its opposite free side biased into engagement with the magnetically entrained developer material 51 on the upper roll 50. Both of the

baffies

42 and 43 extend across substantially the full width of the developer unit 41 and both are preferably formed from non-magnetic, resilient material, such as the aforementioned one mil thick brass shim stock. Moreover, the free side of each of the

baffies

42 and 43 is preferably arcuate so that each presents a continuous edge free, contact surface for engaging the magnetically entrained developer material 51. in other words, the

batfles

42 and 43 shown in H6. 2 desirably have the same self-biasing, self-sealing, non-scraping characteristics as the baffle 17 previously described in connection with FIG. 1. in this embodiment, however, the second baffle I 43 is somewhat more important that a correspondingly positioned baffle would be in the embodiment shown in FIG. 1 because it not only aids in suppressing uncontrolled emissions of toner, but also levels the profile of the magnetically entrained developer material 51 immediately before it is released to cascade across the photoconductively coated drum 45.

As best illustrated by FIGS. 3A and 3B, the uniformity of the development process is improved by leveling the profile of the magnetically. entrained developer material. For example, referring back to FIG. 1 for a moment, there may be substantial variations across the width of the development unit 11 in the thickness or pile height of the magnetically entrained developer material 16 on the upstream side of the metering bar 40 and baffle l7 (FIG. 3A). However, the bias acting on the baffle 17 causes it to redistribute the developer 16 more or Eess laterally from the higher spots to the lower spots, thereby leveling out those variations. Consequently, on the downstream side of the metering bar 40 and baffle 17 (FIG. 38), there is a generally uniformly thick layer of developer material 16 to be presented to the development zone 14.

CONCLUSlON file of the developer delivered to the development zone.

What is claimed is:

l. in a development unit for developing latent electrostatic images on a photoconductor while said photoconductor is moving through a development zone; said unit having a housing, a sump in said housing for storing a supply of developer, means communicating with said sump for adding toner to said developer, and

means including at least one roll spaced from said housing for magnetically entraining and transporting developer from said sump toward said development zone; the improvement comprising a resilient baffle having one side secured to said housing and an opposite, free side with a continuous, edge-free arcuate surface biased into engagement with the developer magnetically entrained on said roll. whereby said baffle provides a seal for suppressing uncontrolled emissions of toner and also levels out any variations in the thickness of the developer magnetically entrained on said roll.

2. The improved development unit of claim I wherein said roll is positioned to brush the magnetically entrained developer against said photoconductor.

3. The improved development unit of claim 2 wherein said baffle is formed from resilient, non-magnetic material and is self-biased to urge said surface against developer entrained on said roll.

4. The improved development unit of claim 1 wherein said roll is positioned to participate in transporting developer from said sump to a position above said development zone where said developer is released to cascade across said photoconductor.

5. The improved development unit of claim 4 wherein said baffle is located to engage the developer nearing said position, whereby the variations in the thickness of the magnetically entrained developer are leveled out just before the developer is released to cascade across said photoconductor.

6. The improved development unit of claim 4 wherein said baffle is formed from resilient, non-magnetic material and is self-biased to urge said surface against developer entrained on said roll.

7. The improved development unit of claim I wherein said baffle is one of a plurality of self-biased. non-magnetic baffles positioned to suppress uncontrolled emissions of toner.

I i i i

Claims

1. In a development unit for developing latent electrostatic images on a photoconductor while said photoconductor is moving through a development zone; said unit having a housing, a sump in said housing for storing a supply of developer, means communicating with said sump for adding toner to said developer, and means including at least one roll spaced from said housing for magnetically entraining and transporting developer from said sump toward said development zone; the improvement comprising a resilient baffle having one side secured to said housing and an opposite, free side with a continuous, edge-free arcuate surface biased into engagement with the developer magnetically entrained on said roll, whereby said baffle provides a seal for suppressing uncontrolled emissions of toner and also levels out any variations in the thickness of the developer magnetically entrained on said roll.

2. The improved development unit of claim 1 wherein said roll is positioned to brush the magnetically entrained developer against said photoconductor.

7. The improved development unit of claim 1 wherein said baffle is one of a plurality of self-biased, non-magnetic baffles positioned to suppress uncontrolled emissions of toner.